Semiconductor image sensors are used to detect radiation such as visible light. A complementary metal-oxide-semiconductor (CMOS) image sensor (CIS) and charge-coupled device (CCD) are applied in various applications such as cameras, mobile phones, and laptops for image capturing. The CIS utilizes an array of pixels in a substrate, including transistors and photodiodes to absorb photons projected toward the substrate and convert the photons into an electrical charge. Analog signals resulting from the electrical charge are amplified and an analog-to-digital converter converts the amplified signals into digital signals. Subsequently, a plurality of processes of color interpolation such as color correction, gamma correction and white balance are performed for image saving or compressing.
In comparison with a front side illumination CIS (FSICIS), a back side illumination CIS (BSICIS) allows incident light to penetrate from a back side of a substrate, i.e., a side opposite to an interconnect structure. In such a way, image sensor operation improves because the BSICIS captures more photons of an image signal than the FSICIS due to reduced reflection of incident light by the interconnect structure.